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Old 07-12-2018, 12:24 PM   #1
SonomaComa
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Join Date: Sep 2015
Location: Sonoma County California
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What's the correct Spark Plugs?

I have a 1969 C-20 with a stock 350 and it does have HEI. I am replacing the spark plugs and plug wires with some MSD #31239 cut to fit wires.
The plugs I purchased at O'Reilly's are R43, the ones I removed are R43S.
Is that going to make a difference? The only difference I see is that the R43S is a little longer and extends farther into the combustion chamber. What would be the advantage of a longer plug?
The plugs I removed look fine, no oil build up or anything out of the ordinary so I don't think a hotter plug would be necessary...?
The AC Delco website even says the R43 plugs are the correct ones. http://parts-catalog.acdelco.com/cat...log_search.php
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Old Yesterday, 11:49 AM   #2
Wrenchbender Ret
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Location: Lenexa, Kansas
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Re: What's the correct Spark Plugs?

The S type plugs (extended tip) came out in the 60,s & were an improvement over the regular plugs. Before long all the manufacturers switched to them. They actually run cooler then the old style plugs. The spark is closer in to the combustion chamber for faster combustion. It is best to use the S type like R43S or R44S. If an engine has the tapered seat use R44TS. The extended tip plugs cannot be used in flat head engines.
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Old Yesterday, 03:43 PM   #3
Dead Parrot
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Re: What's the correct Spark Plugs?

With the HEI, you can gap the plugs to .045 instead of the normal point system .035.
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